The present invention is directed to a diversity antenna system having a plurality of adjacent radiation apertures with different directions of peak radiation. Each radiation aperture preferably consists of an open-ended notch radiator formed as part of a dielectric board separated from the other radiators by conductive septums that cooperate with conductive top and bottom covers to define nonresonant enclosures.
Tapered notch antennas excited by a microstrip feed line are known in the art. The front side of a circuit board has a metallized surface with a tapered notched area etched away to expose the dielectric substrate. The back side of the dielectric substrate has a metallized strip that functions as a microstrip feed line.
The type of diversity discussed herein is spatial diversity, i.e. physically separated antennas. Consider that at a given instant of time the induced signals in each of the physically separated antennas will have different magnitude and phase relative one antenna to the others depending upon the physical spatial separation and the directional characteristics of each antenna with respect to the impinging wave front. Further, reciprocity exists for the system.
Portable communications equipment such as a hand held telephone typically uses a resonant monopole antenna. This antenna produces an omni-directional radiation pattern with peak gain perpendicular to the axis of the monopole. As operating frequencies used by this equipment increase, the number of objects in the environment that can function as a reflector of the radiated energy increases. This occurs because as frequencies increase the wavelengths decrease, and to be a reflector of a radiated wave a reflective object must be at least a substantial fraction of the wavelength. The same signal arriving at an antenna as two or more out of phase signals is known as multipath distortion. Reflections of a signal received out of phase relative to other reflected signals or to a directly received signal give rise to multipath distortion problems. In order to minimize multipath distortion and generally improve the quality of reception at higher operating frequencies, a need exists for an improved antenna suited for use on portable communications equipment which can utilize spatial diversity for improved performance.